Conformational Intermediate of the Amyloidogenic Protein β 2-Microglobulin at Neutral pH

Abstract

Aggregation and fibrillation of β2-microglobulin are hallmarks of dialysis-related amyloidosis. We characterize perturbations of the native conformation of β2-microglobulin that may precede fibril formation. For a β2-microglobulin variant cleaved at lysine 58, we show using capillary electrophoresis that two conformers spontaneously exist in aqueous buffers at neutral pH. Upon treatment of wild-type β 2-microglobulin with acetonitrile or trifluoroethanol, two conformations were also observed. These conformations were in equilibrium dependent on the sample temperature and the percentage of organic solvent present. Circular dichroism showed a loss of β-structures and gain of α-helices. Reversal to the native conformation occurred when removing the organics. Affinity capillary electrophoresis experiments showed increased specific interactions of the nonnative β2-microglobulin conformation with the dyes 8-anilino-1-naphthalene sulfonic acid and Congo red. The observations may relate to early folding events prior to amyloid fibrillation and facilitate the development of methods to detect and inhibit pro-amyloid protein and peptide conformations.